// x and y are a cartesian coordinate system with the center of the planet// at x=0 m, y=0 m. The projectile typically begins its journey at x=0 and// at a given height-above-ground.
x = -700 km
y = r + h

// Drag coefficient equation for a sphere in the subsonic-to-hypersonic environment// See ESTIMATING THE DRAG COEFFICIENTS OF METEORITES FOR ALL MACH NUMBER REGIMES.// R. T. Carter, P. S. Jandir, and M. E. Kress,// 40th Lunar and Planetary Science Conference (2009)// They don't actually display the "quadratic" behavior which occurs below// about Mach 0.8, so this is a curve-fit.// For hypersonic velocities, this is about 0.92, while other authors state that// a constant 0.7 is okay.
Cd[v] :=
{
M0 = v/mach